What Caused the Bright Crater I Now See on the Moon?

Question: Sir Took a picture of the Moon a few days ago and in the lower right hand [corner] a crater was very bright. Was the Moon hit recently?  – Bill

Answer: I am not aware of any recent collisions between our Moon and an object that would create a sizeable crater.  Note, though, that existing craters on the Moon can appear brighter or dimmer as a function of how they are illuminated by the Sun.  For example, a crater can appear quite shadowed one day, then a few days later, when the Sun’s illumination angle has changed to be more direct, appear quite a bit brighter.  This may explain your observation.

Jeff Mangum

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Orbital Period of the Sun in the Milky Way Galaxy

Question: I have read that the Sun is about 15.3 kpc from the centre of the Galaxy and moving at about 230 km/s. I have also read that it takes about 200 million years to orbit the Galaxy. But if the orbit is approx. circular, the period is 2 x pi x radius / velocity which comes out at about 400 million years. What am I missing?  – Bruce

Answer: As you pointed out, the Sun takes about 226 million years to orbit the center of our Galaxy, and it orbits at a speed of about 230 km/s.  The distance from the Sun to the center of our Galaxy, though, is about 8 kilo-parsecs (kpc), which accounts for the factor-of-two overestimate in your orbital period calculation.  As our Galaxy is about 30 kpc in diameter, your calculation would be appropriate for a star on the edge of the Galactic disk.

Jeff Mangum

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Motion of the Stars in the Night Sky

Question: Why do we see the same stars every day of the year in there same location when we orbit?  No way does the Cosmo’s move with us.  – Mike

Answer: In fact, the stars that one can see in the night sky on any given night change as the Earth moves along its orbit around the Sun.  You can test this yourself by noting the location of a bright star on one night at a specific time.  Come back a few weeks later at the same time and note the position of the same bright star.  You will find that the star has moved a bit to the west from its previous location.  This is due to the fact that the Earth has moved a bit along its orbit, which presents a somewhat different view of the stars in our night sky than it did previously.  If you wait an entire year between star position measurements, though, you will find that your star has come back to the same spot.

Jeff Mangum

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Relationship Between Planetary Orbits and Sun Rotation

Question: I was wondering about the relation between the Sun’s own rotation relative to the planets orbit around the sun. Does it also rotate counterclockwise?  Do you have any information about that?  – Rasmus

Answer: Yes, the Sun rotates in a counter-clockwise direction, as viewed from above the plane of the solar system.  This is, as you say, the same direction as the planets orbit the Sun.  As was noted in a previous post regarding the relative motions of the planets and the Sun, this alignment is due to the fact that the Sun and planets formed from the same cloud of gas and dust which itself had residual angular momentum which resulted in a counter-clockwise rotation to the components of our solar system.

Jeff Mangum

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Advantages of a Career in Astronomy

Question: I am doing a school project about astronomy. I was wondering if you could tell me a little about the advantages and disadvantages of being an astronomer.  – Grace

Answer: As I have mentioned in several responses to similar questions about what it is like to have a career as an astronomer in the Careers in Astronomy pages of this blog, there are some clear advantages to a career as a scientist.  These include a regular flow of interesting tasks to do and the flexibility to schedule the work on those tasks using your own discretion.  About the only disadvantage, and this is only a slight disadvantage, is that scientists are not necessarily paid a very high salary commensurate with the long hours that most of us work.  One can make a reasonable living as a scientist, though.

Jeff Mangum

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What Would Happen if a Habitable Planet was Discovered?

Question: If an earth-like planet was discovered by a large US observatory that virtually guaranteed the capability of supporting life, would it be announced to the public straight away? Or would/could the government intervene and likely suppress news of the discovery for some reason? How would other nations observatories and governments likely react if they made such a find?  – Bruce

Answer: I cannot think of any reason why such a discovery would be kept secret.  Such a discovery would likely spur an increase in measurements of this newly-discovered planet, which would likely encourage governments to increase their investments in the science associated with the study of this planet.

Jeff Mangum

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The Density of Matter in a Black Hole

Question: A 10 solar mass object would have 10 solar masses enclosed in a radius of 30 km.   The density of a spherical object scales as M/R3.  Relative to the 10 solar mass black hole, how many times denser would a black hole the mass of the Earth be?  How many times less dense would a black hole of 1 million solar masses be?  – Paul

Answer: As my colleague Cole Miller points out in his description of the properties of black holes and neutron stars, unlike ordinary things (e.g., rocks), which have a size roughly proportional to the cube root of their mass, black holes have radii proportional to their mass.  Taking the event horizon of a black hole as the definition of its outer boundary, the event horizon of a nonrotating black hole the mass of our Sun would have a radius of about 3 kilometers.  This implies that the more massive the black hole is the denser it is, meaning that larger black holes are not very dense.  For example, a one-billion solar mass black hole, which is the type of black hole that is thought to exist at the center of some galaxies (like ours), has an average density just twenty times the density of air.

Jeff Mangum

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A Question About a Career in Astronomy

Question: How can I get involved in a career uncovering the “unexplained” of the universe? I am interested in that particular part of astronomy, but I am not sure if it is too specific, or something that I cannot easily obtain. To put it into perspective, I am interested in astronomy AND astrology (myths, greek mythology, etc). (I bet you are laughing!) I am a 25 year old, and looking to go back to school once and for all. What advice do you have for me?  – Sam

Answer: You should look at the information on my Careers in Astronomy page for information, including questions and answers from people like yourself who are interested in a career in astronomy science in general.  Note that studying the sciences does not exclude the study of those aspects in our culture that sometimes conflict with the results that come from scientific investigation.

Jeff Mangum

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Questions About Cosmology and Catching Near Earth Objects

Question #1: Hello there! Sorry for the previous thing I had sent, it was merely a comment. I am a 16 year old high school student who is interested in the study of the stars and our universe itself.  And I also have a theory to which, I would highly appreciate if you took the time to read it. You know the candle light variable used to measure the distance of us from a certain star? With that being said, there is also the situation of our universe expanding farther away, and the theory of how it will stop and come back to it’s center of where it began, which is where the Big Bang theory comes from. Now, I know this sounds a bit crazy. But hear me out. Since our entire universe is made up of dark matter, also a compound in the creation of our universe with the gas and dust that creates stars, the universe coming back together, crunching into one could cause another Big Bang. In which case, would be the same illusion as a star pulsating it’s light. What if we are only specs of particles and molecules created to make one big star? What if our whole universe if just one star as we know it, and there are billions upon billions of stars, that make up universes?  – Rachel

Answer #1: All theories, whether they be to explain the evolution of the universe or the properties of a star, require measurements to support them.  What measurements support your theory?  This is the key to any scientific investigation that involves theory which must ultimately be supported by observations.


Question #2: Also, I’d like to mention that I have an idea for a device that could be placed a certain distance away from Earth, enough not to mess with the gravitational pull, and take the near earth objects that could be potentially dangerous by coming to close and crashing in Earth. What if they made a device to take these potentially dangerous items and drag them away from Earths surface, and had a inside that could destroy the items inside? This device could also be used for meteorites, to pull them away from the Earth’s gravitational pull. Also, with delittering the area, you could catch more light in telescopes and would be allowed to possibly see things even farther than we ever have. Please message me back, telling me what you think!

Answer #2: How would this device collect meteoroids and potentially dangerous asteroids?  Note that the sheer number of meteoroids and asteroids that this device would need to collect would make any “scooping” device not practical.


Jeff Mangum

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In What Direction Does the Outflow from a Quasar Go?

Question: Thank you for answering! Is the supposed spinning the reason all the body’s caught in the pull stay in a synchronized belt around it? If so, where does a quasar emit? “North and south?” Or anywhere it pleases? I know very little known, but these questions are the reason I can’t sleep at night.  – Nathan

Answer: Quasars emit their outflows which are suggested to coincide with the rotation axis of an embedded black hole.  This direction is preferred as it represents the direction where the angular momentum is lowest, thus allowing the outflow material to propagate away from the black hole.

Jeff Mangum

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